Organomagnesium compounds are known to be useful in a wide variety of chemical reactions. As reagents, organomagnesium compounds are used for the reduction of ketones, the metalation of aromatic compounds, and the alkylation of metal halides or oxides. As catalysts, organomagnesium compounds are useful in the dimerization and polymerization of olefins, see British Pat. No. 1,251,177, the polymerization of epoxides, see U.S. Pat. No. 3,444,102, and the preparation of telomers, see U.S. Pat. No. 3,742,077. While they perform many of the functions performed by Grignard reagents, organomagnesium compounds, owing to differences in electronic and steric factors, are more reactive toward certain types of compounds. For further discussion of organomagnesium reactions, the reader is referred to U.S. Pat. Nos. 3,646,231 and 3,822,219.
Some of the most useful organomagnesium compounds are dialkylmagnesium compounds. Although some are insoluble in hydrocarbon solvents, it has been shown that those containing branched-chain alkyl groups, cyclic alkyl groups, or straight-chain groups of five carbons or more are indeed soluble. Examples include di-tert-butylmagnesium, di-sec-butylmagnesium, di-n-amylmagnesium, methylisobutylmagnesium, ethylisobutylmagnesium, di-n-hexylmagnesium, dicyclohexylmagnesium, di-n-heptylmagnesium, etc. In addition, certain combinations of straight-chain lower alkyl groups have also been found to be soluble--n-butylethylmagnesium, n-butylmethylmagnesium, and n-propylmethylmagnesium.
Unfortunately, most of the resulting solutions are highly viscous. This detracts from the utility of the compounds since their viscosity renders them less reactive as reagents and catalysts and more difficult to handle and transfer. In addition, the viscosity of the solutions makes it difficult to prepare the compounds in a form free of halides and other undesirable solids. Following the procedure described in Glaze and Selman, Journal of Organometallic Chemistry, Vol. 5, p. 477, (1967), and W. N. Smith, Journal of Organometallic Chemistry, Vol. 64, p. 25 (1974), dialkylmagnesium compounds are conveniently prepared by the reaction between metallic magnesium and the appropriate alkyl chloride in the desired hydrocarbon solvent. The by-product of this reaction is magnesium chloride, which is insoluble in hydrocarbons. Both the magnesium chloride and any unreacted magnesium metal, which is frequently used in excess, remain as solid matter suspended in a viscous liquid. The viscosity prevents an easy separation of the solution from the solids, requiring instead centrifuging equipment or the like or a long period for the solids to settle.